I'm looking for some basic information. Basic as in "at the base". Like if you know the ASM or C pointer background of what a variable and function call really are, you more easily understand any language.

I've lived at the bottom of a hill, i.e. with bad TV reception. The switch from analogue to digital has basically ruined things for me, because it's quite easy to cope with a grainy picture and occasionally slightly hissy sound (but rarely - FM's damn resilient) but impossible to cope with the blockiness and intermittent loss of soung with DVB-T.

How well has the transition to digital satellite gone? When it's pissing down with rain, will I just get little lines on the screen like on my old analogue receiver

I am using over the air digital signal with a D->A converter box, I found that a cheap (about $30) Walmart TV amplifier made a big difference in signal. Save the receipt, be gentle opening the package (I used a razor) and if it does not work in your particular case then just return it...

DVB means Digital Video Broadcasting Symbol rate is the speed at which the bytes are transferred. It's usually in Baud, so if you have ever played with a classical modem (14K4 for example, it means 14400 Baud) you should know something about it. Channels are multiplexed into a transponder. For example the Astra 1 at 19.2 E satellite (default here in NL) has a transponder 97 (12344 MHz, horizontal) with 25 channels on it (13 TV and 12 radio channels). These channels all have a different addresses (I believe they are called PID's). Video signals have even 2 (one for audio and one for video). There is some system that tells the receiver what addresses are taken at the moment and some system that creates a start (an adress 0). From the start point each channel is send when it's time slot is there. The receiver simply waits until the correct time slot and puts the data into the input buffer. Most satellites nowadays use Mpeg 2 encoding to compress the data. Due to this there is a lot of spare space on the satellite, although Astra 1 contains about 700 channels (radio + TV). What most people (including me) refer to as a satellite is usually a bunch of satellites. They are positioned in a geostationary orbit within an angle of 0.1 degree. The receiving disk people use is to small to distinguish between them, so it appears as one sat. The opening angle of a 60 cm dish is about 2 degrees. This determines the effective resolution. I believe communication satellites (sattelite groups) are never spaced less than 3 degrees apart, so it's quite easy to distinguish the sat. With a bigger disk (80 cm, 1 meter) you have a smaller opening angle, so you receive less noise and thus effectively a stronger signal. A bigger disk also has a larger area, and thus the absolute signal strength is higher as well. Off course you should not increase to a disk with an opening angle of less than 0.1 degree, or you won't be able to receive the complete group. The Astra 1 satellite (or group of satellite's if you will) sends at 10 to 12 GHz, with two polarisations (Horizotal and vertical antenna's give different signals). The frequency is way to high to send over a cheap cable, so it's downconverted. This is done by the LNBC, the small box on the receiving disk. This thing does a couple of tasks:

It contains the antenna's (two of them at 90 degree angles, one for the horizontal signal and one for the vertical signal)

It contains the converter to decrease the signal frequency to between 1 and 2 GHz

It receives data from the set top box (the thing in the living room) which polarization and which frequency band (high or low) it should take.

It selects the correct polarisation and frequency band and sends it over the cable

This LNBC is quite an interesting thing. It's a high frequency device (up to 12 GHz) but it is cheap (you can have one for less than EUR 20). Most of the parts are etched into the PCB. The signal is send over a relatively cheap (like 1 euro per meter) to the set-top box. There is a great variety in these: simple ones, versions with recording harddisks, versions that can display two different channels (PIP or different outputs), versions for HD signals. Even versions with Linux as main operating system (the Dreambox). In the receiver is usually a smartcard with encryption data. This can be directly into the receiver, but sometimes there is a PCMCIA-like "sleeve" (a module) in the receiver with the card in that. The receiver (or the module) decrypts the signal with the data from the smartcard. Both ways usually work There is a strange thing with brands: While Phillips and Nokia make satellite set-top boxes (sometimes called receivers) the best brands (IMHO) are not very well known in other fields (Topfield is a good brand. I have not heard of a non-"digital set-top box" product from them. They do have quite good cable receivers.). I am not sure why this is. Phillips receivers in the Netherlands are very locked-in devices and a Nokia receiver is something you

I always thought satellites used circular polarizations (clockwise and anticlockwise) rather than horizontal/vertical because having the signal reflect off a surface has a very nasty tendency to twist the signal about. And circular polarizations make the orientation of the LNB less of an issue...

The LNB does two things - besides downconverting the signal, it also amplifies it since the receiver box can be far away. Incidentally, the LNB is an active device, but it gets its power (and polarization switching)

Both types of polarization are used, depending on the satellite owner's preference. Intelsat is almost strictly circular on their transcontinental links, while the majority (if not all) domestic US birds are linear polarization.

Not all LNBs can do active polarity switching. LNBs for fixed VSAT terminals and fixed recieivers have their polarity adjusted by manually turning the feedhorn.

Symbol rate is the speed at which the bytes are transferred. It's usually in Baud, so if you have ever played with a classical modem (14K4 for example, it means 14400 Baud) you should know something about it.

DVB Satellite signals are specified in Megasymbols/sec, not baud. A DVB carrier is specified by the a few parameters:

Center frequency (either in the actual downlink frequency from the satellite or in L-Band after the LNB)Symbol rate (In kilo or megasymbols/sec)Modulation (BPSK, QPSK, 16PSK, 32PSK)FEC rate (1/2, 3/4, 7/8)

Once you lock onto the stream, then you can dig out the various PIDs.

Channels are multiplexed into a transponder.

Not multiplexed onto a transponder, but multiplexed into a carrier. A transponder can have multiple carriers, each carrier can have mutliple channels (separated by PIDs). Transponders are just a chunk of raw spectum on the satellite, each usually either 36 or 72MHz wide.

Most satellites nowadays use Mpeg 2 encoding to compress the data.

Technically, it's not the "satellite" that encodes the signal. The satellite is just a "radio bent pipe" in space. The ground station is what encodes the signal, the satellite just retransmits what it gets. MPEG-2 is the prevalent digital compression mode, but more services are going to MPEG-4, especially for HD video and on DVB-S2.

Not trying to be pedantic, just making sure the right terms are used. Having been in the satellite industry for 10+ years now, those things annoy me just as much as someone saying "I've got 250GB of memory in my computer"

The definition is technically right, but wrong for the common lingo. Baud means "symbols per second." Hertz means "per second." You'd never hear anyone in the satellite industry say anything other than megasymbols per second (usually Msps from what I see, but some people have a hard-on for using Ms/s or such to avoid having the "/" be represented by a letter). Hertz isn't limited to frequency, but could be indicating symbols as well, but you'd never see anyone say "megasymbol hertz" or such, though tech

Yea, it is geeky. Plus, you can watch lots of TV channels you may not normally get, from countries you didn't know about, or in languages you didn't know existed.
Search for Free to Air satellite TV. Below is a good starting point:
http://www.ftalist.com/index.php [ftalist.com]

AAA members can get 2 gallons of fuel free when the call the tow-truck. At 75$ a year membership fee, just get 1000 memberships and you can ask for 4000 gallons for $75000. And if you put it on the Discover card, you get 1% cash back too.

Over $127,000 per lb. A gallon of fuel is about 6 lbs depending on what kind. It's not too far from $1 million/gallon. btw, the cost of orbital launch is about $10,000 per lb - these guys must be making a ton of profit. The stock price for MDA agrees [quotemedia.com].

I can only assume that a nontrivial chunk of the price tag is for the "expertise required to safely approach a moving satellite and introduce additional fuel, without crashing into it, breaking off any important solar panels/antennas/widgety bits, or otherwise mucking it up.

Sort of a very high end version of the classic techie contractor invoice: "'Typing a one line command, $1' 'Knowing which command to type, $400/hr+travel'"

Not quite as good as it looks assuming they can sell all 2000Kg for $560 million gross

The craft carry s 2000Kg fuel but will masses 6000Kg I recall it costs $25000 to high orbit so were talking at least $150 million to get the fuel up there it will then have to perform at least 6 satellite rendezvous (Intelsat want 5x200Kg drops done, someone else may want one 1000Kg drop). Before that they have to design and build the thing and insure it against going Bang at an inopportune moment. They stand to make m

Yes, you need fuel to move the vehicle around. Without propulsion thrusters and these station-keeping manoeuvres, perturbations in the gravitational field of Earth and other solar system objects will cause the satellite to drift from its orbit.

There isn't much, but there is still the occasional molecule bumping around( Even between galaxies the density ranges between 1 atom per cubic centimeter to 1 atom per cubic meter), add solar winds, the moon, slight variations in gravitational pull because the earth is unfortunately not a perfect sphere of uniform density, let's through in the galactic core for good measure since hey gravity goes to infinity. Oh and were not perfect at putting satellites into orbit so they may slowly drift into each other

Geostationary orbits aren't inherently stable. They're far enough from the Earth to be subject to significant gravitational influence from the Moon, Sun and Jupiter. Depending on their mass, satellites in geostationary orbit might have to expand as many as 100 kilograms of propellant per year for station-keeping purposes. This mass is reduced significantly if you make satellites with higher efficiency, lower thrust propulsion systems, such as ion thrusters, as opposed to chemical thrusters that are mostly i

There shouldn't be much 'decay' in geostationary orbit. Its not like there is atmospheric drag like you get in LEO

No, there isn't. What's happened with this drift is that the non-uniformity of the Earth's mass distribution creates a non-uniform gravitational field. This, combined with perturbations from the moon's orbit (and even other gravitational bodies such as the Sun and Jupiter) means the orbit is not a perfect predictable ellipse and it shifts slightly over time. Consequently, its period become slightly more or slightly less than the 23h, 56m, 4s rotational period of the Earth (http://en.wikipedia.org/wiki/Sider

The articles I read are sparse in details, but you must remember that fuel was put into the tanks somehow before launch. They will probably use the same connector to refuel.

Fueling up the satellite is one of the last activities before launch, because it's so dangerous. Besides being explosive, hydrazine is extremely toxic. So toxic that technicians use astronaut suits [physorg.com] to do it.

The connector may be there, but the ability to connect to it in freefall is quite different from the ability to connect to it while it's an inert mass on the ground.

The only way this works is if someone had the foresight to presume it might be refueled on-orbit, and the authority to require the connector -- and the rest of the satellite; you don't want an expensive solar panel in the way when the service droid is trying to grapple onto the cleat -- to be designed to allow it.

Since the earth is "oblate", which means flattened at the poles, the orbit over the equator isn't stable, it slowly gets inclined at a rate of approximately one degree per year. So-called "north-south" maneuvers are needed to keep the orbit exactly over the equator.

There are also "east-west" maneuvers. The earth is not perfectly symmetrical, rock is denser at some parts than at others, that's why we have ocean and continents. Denser rock sinks, lighter rock floats. The asymmetric gravity field from this difference in density pulls the satellite away from its intended location.

Inclination correction uses about 90% of the fuel needed for station keeping. This means that often older satellites are used in "inclined orbit", when the owner stops doing north-south maneuvers and lifetime can be extended, with some degradation in the services, because the antennas need to track the daily excursion of the satellite north and south of the equator.

Finally, some fuel is needed for deorbit. In order to keep the geostationary orbit uncluttered, the last drops of fuel are used to send the satellite to a "graveyard" orbit, a few hundred kilometers higher up.

Here's what I want to know... Were these satellites built with provisions (such as connectors/etc) to allow for in orbit refueling? If so, it seems perfectly reasonable to have a small spacecraft mosey up to the satellite and give it a top off. However, once you start cutting into the thermal blankets to expose the fuel lines, I have to wonder what their success rate is going to be. I have to imagine if they're embarking on this adventure they've figured out how to do this with some reasonable rate of su

Erm, no. An oblate spheroid has a stable orbit about its equator (gravity is lower on the surface because the surface is higher there; but at a constant radius there's more mass under anything that's over the equator so gravity is higher there than at the same radius over the poles).

But Earth isn't an oblate spheroid. It's bigger in the southern hemisphere. Hence inclination of the orbit. It's also not circular at the equator, and not a constant density. The gravitational field is lumpy. Gradients all

Intelsat's Galaxy 15 satellite was successfully rebooted in December and is responding to commands and no longer interfering with other satellites.
http://en.wikipedia.org/wiki/Galaxy_15 [wikipedia.org]

Intelsat's Galaxy 15 satellite was successfully rebooted in December and is responding to commands

Yes, but there are other zombie satellites up there. Galaxy 15 was in the news because it failed with its transmitters working, so it caused interference in communications, but some other satellites are drifting around GEO, creating the need to maneuver active satellites to avoid collisions.

Besides, the ability to refuel and tow away satellites means that there is less need to keep fuel for deorbit. One needs to keep some amount of fuel in reserve to move the satellites to an orbit higher up at the end of i

This story just triggered my geekometer. To me, this step seems so cool, that we now have space gas attendants and junk men. It makes me feel as if some of the science fiction that I've read is not so far away after all.

With refuelling, it is much, much cheaper to operate a satellite for a longer time. You get extended lifespan for a fraction of the cost that would be needed to build and launch another satellite as replacement. Sure, the initial cost of developing and lauching the service vehicle is high, but divide it by the number of satellites it can service and you get a really small amount. Also, it solves the problem of 'zombie' satellites, as recently exemplified by Galaxy 15.

Some people went on more than one mission, so it's not as easy as 9*3.
Turns out that I got it wrong anyway. There were only 24. 12 landed on the moon (Apollo 11-12, 14-17). 14 Went to the moon without landing (Apollo 8, 10-17 with 3 on 8, 10 and 13 and 1 on 11-12, 14-17). I added those two together to get to 26 but forgot that Young and Cernan were in both lists (Young on 10 and 16, Cernan on 10 and 17).
http://en.wikipedia.org/wiki/Apollo_Astronauts [wikipedia.org]

Hello my northerly neighbors! I have a question for you all. I've been doing some research into the Canadian space industry and so far what I have found has impressed me. It seems that the space industry in Canada, while small, is quite ambitious and capable. You all have a well developed microsat industry. You have a good track record for space robotics (just look at all the stuff you added to the ISS). Hell, you even have a Canadian astronaut program, not many countries can claim that.

Most people don't know or care much about the space industry, and the geeky types think it's cool. Due to a good TV miniseries I suspect most people know about the Avro Arrow than about the current contributions to space exploration and industry.

To be clear, what they are doing is sending up a 2nd satellite with full hydrazine tanks which attaches itself to the aging satellite. No fuel transfer takes place, as you might have expected because the satellite tanks don't include caps removable in orbit.

The new bolted on satellite then carries out station keeping maneuvers until it's own tanks are depleted, or until the satellite owners give up on it (in which case they typically use a little fuel to send it to a higher graveyard orbit).

Not according to this article [spacenews.com]: "the refueling vehicle would dock at the target satellite’s apogee-kick motor, peel off a section of the craft’s thermal protection blanket, connect to a fuel-pressure line and deliver the propellant"